BACKGROUND: Proper positioning of a patient during radiotherapy treatment delivery is crucial for successful implementation of a treatment plan ensuring maximum dose to the target while minimising the dose to the normal tissues. The purpose of this study is to assess the set up errors and to determine the optimal Clinical Target Volume (CTV) to Planning Target Volume (PTV) margins for Cervical Carcinoma patients treated in supine position by Image guided Radiotherapy. METHODS AND MATERIALS: 219 kVCBCT images were acquired for 10 cervical cancer patients treated with Conformal External Beam Radiotherapy using Image Guidance. Daily set–up errors along the three translational directions were analysed, evaluated for systematic and random errors and optimal CTV–PTV margin determined. RESULTS: Corresponding CTV–PTV margins in the X, Y and Z directions were 0.7cm, 1.7cm and 0.4cm respectively. CONCLUSION: IGRT is imperative for ensuring adequate target volume coverage and eliminating geographic miss in IMRT treatment.